Analysis of dynamic tensile fracture behavior of rocks during spalling tests using the 3-D finite-discrete element method

抄録

Understanding the dynamic tensile fracture behavior of rocks is a critical issue in rock engineering, particularly in contexts such as blasting operations, seismic events, and impact-induced failures. Conventional Brazilian disk tests are widely used for estimating tensile strength, but when the loading rate exceeds approximately 20 s⁻¹, these tests frequently result in shear fractures near the loading ends instead of the desired central tensile failure. This limitation has prompted the adoption of spalling tests, typically conducted with Hopkinson bar systems, as an alternative means of evaluating the dynamic tensile strength of rocks. However, existing evaluation methods for spalling tests often produce inconsistent results, not only in the determination of tensile strength but also in the estimation of strain-rate conditions. Such discrepancies make it difficult to achieve a clear and reliable understanding of the strain-rate dependency of tensile strength, which is essential for both theoretical interpretation and engineering applications. This is the summary of the original paper published by Min et al. (2023), which received the Best Paper Award from the Japanese Society for Rock Mechanics (JSRM). In the study, a three-dimensional finite–discrete element method (3D FDEM) is employed to simulate the dynamic fracture process in spalling tests using granite specimens. The numerical simulations successfully reproduce both the characteristic fracture patterns and the free-surface velocity responses observed in corresponding laboratory experiments. Furthermore, the modeling results provide insights into the sources of discrepancies among existing evaluation approaches, clarifying the conditions under which they diverge. By integrating experimental evidence with advanced numerical simulation, this framework contributes to improving the accuracy and reliability of dynamic tensile strength assessment, while also providing a more robust interpretation of strain-rate dependency in rock tensile behavior.